The influence of static electricity on the production and assembly of components
Generally, the positive and negative charges carried by any object are equal. When friction and contact with other objects are separated due to mechanical action, the frictional electrification sequence of the two objects is different, and the positive charge accumulates on one object, and the other An object accumulates negative charges, generates static electricity on each object, and forms an external electrostatic field. Rubbing two substances against each other is a way to generate static electricity, but it is not the only way. Like spraying operations, water droplets absorb negative ions in the air to promote the formation of an electric double layer on the surface, which can also generate static electricity. The results of modern scientific research show that electrical effects, piezoelectric effects, and electrostatic induction of conductors (or dielectrics) can all generate static electricity.
Static electricity hazards are caused by static electricity and static sparks. Among static electricity hazards, the most serious electrostatic discharge (ESD) causes fires and explosions of combustibles. It is often said that the measures to prevent the occurrence of static electricity are generally to reduce the flow rate and flow rate, transform the process links with strong electrification, and adopt equipment materials with less electrification. The *simple and *reliable way is to ground the equipment with a wire, so that the charge can be introduced into the ground and avoid static electricity accumulation. Careful passengers will probably find that discharge brushes are installed on both sides of the wingtips of the aircraft and the tail of the aircraft. When the aircraft is landing, in order to prevent passengers from getting electric shocks when they disembark, most of the aircraft landing gears use special grounding tires or grounding wires. In order to discharge the static charge generated by the aircraft in the air. We often see an iron chain at the rear of a tanker truck. This is the grounding wire of the truck. Appropriately increase the humidity of the working environment to allow the charge to be discharged at any time, and it can also effectively eliminate static electricity. This is the reason why it is not easy to do an electrostatic test in humid weather. The antistatic agent studied by the researchers can eliminate the static electricity inside the insulator well. However, there are two sides to everything. For static electricity, as long as you understand its temper and use its strengths and avoid weaknesses, it can also serve humanity. For example, electrostatic printing, electrostatic spraying, electrostatic flocking, electrostatic dust removal and electrostatic sorting technologies have been widely used in industrial production and daily life. Static electricity has also begun to show its skills in many aspects such as desalination of seawater, spraying of pesticides, artificial rainfall, and low-temperature freezing, and even electrostatic devices such as electrostatic feeders have been installed on spacecraft.
Static electricity and its influence on the production and assembly of components
1. Work clothes: ordinary work clothes (made of chemical fiber and pure cotton) worn by operators can generate 0.2-10 microcoulombs of charge when rubbing on the work surface and work chair, and can generate an electrostatic voltage of more than 6000 volts on the surface of the clothing and make The human body is charged. When the operator holds the integrated circuit in contact with the components placed on the work clothes or the work surface, it can cause electric discharge. Due to the different contact potentials of the lead wires of the components and the extremely thin dielectric strength of the chip, it is easy to cause the breakdown of the device dielectric.
2. Work shoes: The insulation resistance of general work shoes (rubber or plastic soles) is as high as 1x1013 ohms or more. When rubbing against the ground, static charges will be generated to make the human body and the clothes wear static electricity. Investigations show that there are not many cases of component failure caused by static electricity generated by friction between work shoes and the ground. However, due to its high insulation resistance, the static electricity carried by the human body cannot leak quickly, which has a negative impact on the production of components.
3. Resin and varnish encapsulation surface: Many components used in the electronics industry need to be encapsulated with high-insulation resin and varnish. After these devices are placed in the package, due to friction during transportation, electrostatic voltages of hundreds of volts or more can be generated on their surfaces, causing device chip breakdown.
4. Various packaging and containers: packaging and component boxes (boxes) made of PE (polyethylene), PP (polystyrene), PUR polyurethane, ABS, polyester and other polymer materials can be caused by friction and impact. Generate static charge and adversely affect the packaged devices.
5. Terminal table and work table: When the surface of the terminal table and work table is subjected to friction and generates static electricity, it can discharge the electronic devices placed on it.
6. Various insulating floors: waxed and polished floors, rubber sheets, etc. can generate static electricity due to friction. In addition, because of its high insulation resistance, when the operator is charged with static electricity, it will not leak the static charge in a short time.
7. Incubator: The hot circulating air flow in the incubator and the friction of the box body generate a large amount of static charge, which is very unfavorable for the thermal drying of the device.
8. CO2 low temperature box: In the cooling box used, CO2 vapor can generate a large amount of static charge.
9. Air compressor: The spraying, cleaning, painting, sandblasting and other equipment of the air compressor can generate a large amount of static charge due to the violent air flow or the friction between the medium and the nozzle. The charged medium can cause damage when it comes into contact with electronic devices.
10. Certain electronic production equipment: high-voltage transformers and AC/DC circuits in certain component assembly equipment such as soldering irons, wave soldering machines, etc. can induce electrostatic voltage on the equipment. If no electrostatic leakage measures are taken, the components may fail during the assembly process.
The harm caused by static electricity in industrial production
The generation of static electricity is inevitable in industrial production, and the damage it causes can be attributed to the following two mechanisms:
One: The harm caused by electrostatic discharge (ESD):
1. Causing malfunction or malfunction of electronic equipment, causing electromagnetic interference.
2. Break down integrated circuits and precision electronic components, or promote the aging of components, and reduce the yield of production.
3. High-voltage electrostatic discharge causes electric shock, endangering personal safety.
4. It is easy to cause explosion and fire in the production place where there are many flammable and explosive products or dust and oil mist.
Second, the harm caused by electrostatic attraction (ESA):
1. Electronic industry: absorb dust, cause pollution of integrated circuits and semiconductor components, and greatly reduce the yield.
2. Film and plastic industry: make the film or film roll up unevenly; the film and plastic disk are contaminated with dust, which affects the quality.
3. Paper-making and printing industry: Paper is unevenly wound, inaccurate overprinting, pollution is serious, and even the paper sticks, which affects production.
4. Textile industry: causing hazards such as fluttering of roots, broken ends of entangled flowers, and tangled yarns.
The harm of static electricity is obvious to all. Now more and more manufacturers have begun to implement various levels of anti-static measures and projects. However, it is necessary to realize that a perfect and effective anti-static project should be based on the actual conditions of different enterprises and different operating objects, and corresponding countermeasures should be formulated. Anti-static measures should be systematic and accurate, otherwise, it may get twice the result with half the effort, or even cause destructive reaction.
Electrostatic safe operation
To a large extent, electrostatic protection is the issue of raising the awareness of electrostatic protection, and the level of knowledge of static electricity of all personnel contacting electrostatic sensitive devices has improved, so it is very important to carry out electrostatic safety operation and electrostatic protection technology education. In the US military standards and Chinese standards, there are clearly stipulated six aspects including electrostatic protection grounding, electrostatic protection personnel and electrostatic protection equipment of the site environment, and routine maintenance of electrostatic detection instruments and protective measures.
1. Electrostatic protection grounding
The anti-static system must have an independent and reliable grounding device. The grounding resistance should generally be less than 10 ohms. The burying and detection method should meet the requirements of GBJ79: the anti-static ground wire must not be connected to the power neutral line and must not be shared with the lightning protection ground wire. Use three Phase five-wire system power supply, its earth wire can be used as an anti-static ground wire (but the neutral ground wire must not be connected)
2. Electrostatic protection of the site environment
For the ground walls and ceilings of the anti-static work area, national standards require that anti-static materials should be selected to have good anti-static performance. The use of ordinary insulating materials is prohibited.
3. Electrostatic protection of personnel
The human body can generate static electricity with a voltage of tens of volts to tens of thousands of volts in daily activities and production operations, and the discharge process is extremely short, so the energy released during the discharge process can reach tens of watts, which is enough to cause the micro area of the chip to burn out or The SiO2 film breaks down, so the personnel entering the anti-static work area should be equipped with anti-static clothing and anti-static shoes, and the equipment maintenance personnel should also be equipped with an anti-static wrist strap.
4. Electrostatic protection of equipment
The anti-static safety workbench is the basic part of the anti-static work area. It consists of the workbench anti-static table mat, wrist strap joints and grounding wires. It is not allowed to pile plastic, rubber, cardboard, glass, etc. on the static safety workbench. The sundries that generate static electricity, drawings, materials, etc. should be placed in an anti-static document bag. The seat cushion cover should be electrostatically conductive and connected to the static ground. If necessary, the workbench should be equipped with an ion wind static eliminator, and the seat Anti-static floor mats can be laid underneath. During the development and production of electronic equipment, all containers for storing and revolving electrostatic sensitive devices (SSD) should have electrostatic protection properties, and metal and ordinary plastic containers are not allowed.
5. Electrostatic detection instrument
Equipped with relevant static detection instruments to test personnel, equipment and various protective measures at any time or regularly to ensure the effectiveness of protection.
6. Routine maintenance of protective measures Any anti-static measures are not permanent. Correct and proper maintenance needs to be carried out regularly in daily use to ensure that it can effectively extend its service life and reduce costs.